Evaluation system and method for evaluating vulcanized rubber material deterioration by ozone

ABSTRACT

A test sample of a vulcanized rubber material is placed under a preset placement condition in a fixing frame in a test tank having a predetermined ozone concentration, and detection data is acquired by detecting, over time, with a laser sensor disposed facing a surface of the test sample that has been placed in the test tank, a distance from the laser sensor to the surface of the test sample; and determining a change in a surface state of the test sample between a plurality of points in time by analyzing, with a computation device, the detection data that has been acquired. Such evaluation method and evaluation system for evaluating ozone deterioration of a vulcanized rubber material can accurately determine a change over time in ozone deterioration while reducing working man-hours.

TECHNICAL FIELD

The present invention relates to an evaluation method and an evaluation system for evaluating ozone deterioration of a vulcanized rubber material, and particularly relates to an evaluation method and an evaluation system for evaluating ozone deterioration of a vulcanized rubber material which can accurately determine a change over time in ozone deterioration while reducing working man-hours.

BACKGROUND ART

So-called ozone cracks occur in various vulcanized rubber products such as tires. When ozone cracks become large, the performance and service life of the rubber product are affected. As a method for evaluating the ozone deterioration of vulcanized rubber, a static ozone deterioration test that is specified in JIS K 6259-1: 2015, “Determination of Vulcanized Rubber and Thermoplastic Rubber Ozone Resistance” is widely known. In this test method, a test coordinator checks the deterioration state of a test sample disposed under a predetermined ozone concentration atmosphere at predetermined time intervals. That is, the presence or absence of cracks in the surface of the test sample, the state of the cracks, the size of the cracks, and the like need to be recorded at predetermined time intervals by the test coordinator. In addition, due to a difference in sensory judgment between test coordinators, variations in the evaluation results of ozone resistance occur.

A method for quantitatively evaluating ozone deterioration of vulcanized rubber has been proposed (see, for example, Patent Document 1). In the evaluation method proposed in Patent Document 1, a vulcanized rubber test piece, which has been elongated to a certain degree, is exposed to an ozone atmosphere for a predetermined amount of time, and then the surface state of the test piece is observed with an optical microscope or the like while the test piece is kept in an elongated state. Then, after specifying an image capture region of the surface of the test piece, images of the image capture region are captured by a video camera or the like. Next, the ratio of the area occupied by ozone cracks to the area of the image capture region is calculated by processing the captured images (upper left column to upper right column on page 2 of the specification). In this method, a quantitative change in the area in which ozone cracks have occurred can be determined. However, it is necessary to observe the surface state of the test piece with a microscope or the like. In addition, when performing observation with a microscope or the like, it also becomes necessary to remove the test piece from a test tank filled with ozone. Therefore, there is room for improvement in the determination of a change over time in ozone deterioration while reducing the number of working man-hours.

CITATION LIST Patent Literature

Patent Document 1: JP H04-109142 A

SUMMARY OF INVENTION Technical Problem

An object of the present invention is to provide an evaluation method and an evaluation system for evaluating ozone deterioration of a vulcanized rubber material that can accurately determine a change over time in ozone deterioration while reducing the number of working man-hours.

Solution to Problem

In order to achieve the object described above, a method, for evaluating ozone deterioration of a vulcanized rubber material of the present invention, in which a test sample of a vulcanized rubber material is placed under a preset placement condition in a test tank having a predetermined ozone concentration and a change over time in a surface state of the test sample is determined, includes acquiring detection data by detecting, over time, with a laser sensor disposed facing a surface of the test sample that has been placed in the test tank, a distance from the laser sensor to the surface; and determining a change in the surface state of the test sample between a plurality of points in time, based on the detection data.

A system, for evaluating ozone deterioration of a vulcanized rubber material, in which a test tank is maintained at a predetermined ozone concentration and a fixing frame enables placement of a test sample of a vulcanized rubber material under a preset placement condition in the test tank, includes a laser sensor disposed facing a surface of the test sample that has been placed in the test tank; a storage unit into which detection data of a distance from the laser sensor to the surface, which is detected over time by the laser sensor, is input; and a computation device configured to execute a predetermined detection data processing program, a degree of change in a surface state of the test sample between a plurality of points in time being calculated by the computation device, based on the detection data.

Advantageous Effects of Invention

According to the present invention, with the test sample of the vulcanized rubber material to be evaluated disposed in the test tank having a predetermined ozone concentration, by using the laser sensor disposed facing the surface of the test sample, the distance from the laser sensor to the surface of the test sample is detected over time and detection data is acquired. Then, the change in the surface state of the test sample between a plurality of points in time is determined on the basis of the acquired detection data, so there is no need for the test sample to be removed from and placed into the test tank each time the surface state of the test sample is to be checked. In addition, observation of the surface of the test sample with a microscope or the like is also unnecessary. Furthermore, since a change over time in the surface state of the test sample can be determined based on the acquired detection data, not only the planar size of ozone cracks but also the depth and volume of ozone cracks can be determined. Therefore, according to the present invention, it is possible to accurately evaluate a change over time in ozone deterioration while reducing the number of working man-hours.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram illustrating an evaluation system of the present invention for evaluating ozone deterioration of a vulcanized rubber material with a test tank viewed from the side.

FIG. 2 is an explanatory diagram illustrating a front view of the inside of the test tank in FIG. 1.

FIG. 3 is an explanatory diagram illustrating a plan view of the inside of the test tank, a laser sensor, and a camera device illustrated in FIG. 1.

FIG. 4 is an explanatory diagram illustrating a front view of a change over time in a surface of a test sample.

FIG. 5 is a graph illustrating a change over time in the volume of cracks that have occurred.

FIG. 6 is a graph illustrating a change over time in the area of cracks that have occurred.

FIG. 7 is an explanatory diagram schematically illustrating data stored in a storage unit.

FIG. 8 is an explanatory diagram illustrating a plan view of a modified example of the test tank illustrated in FIG. 3.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an evaluation method and an evaluation system for evaluating ozone deterioration of a vulcanized rubber material according to embodiments of the present invention will be described with reference to the drawings.

For the evaluation method for evaluating ozone deterioration of a vulcanized rubber material of the present invention, an ozone deterioration evaluation system 1 (hereinafter referred to as evaluation system 1) of the present invention exemplified in FIGS. 1 to 3 is used. The evaluation system 1 includes a test tank 2, a fixing frame 3 to which a test sample S of a vulcanized rubber material to be evaluated is attached, and an ozone injector 4. Furthermore, the system 1 includes a laser sensor 5 disposed facing the surface of the test sample S that has been placed in the test tank 2, a storage unit 9 into which detection data 5 x from the laser sensor 5 is input, and a computation device 8 configured to execute a predetermined detection data processing program. A computer including a CPU and a memory may be used as the computation device 8 and the storage unit 9. A monitor 7 is connected to the computer, and the detection data 5 x (5 a, 5 b, 5 c, . . . ), a calculation result from the computation device 8, and the like are displayed on the monitor 7.

The system 1 of this embodiment further has at least one camera device 6.

Digital image data 6 x (6 a, 6 b, 6 c, . . . ) captured by the camera device 6 is input to the storage unit 9. In addition, a predetermined image data processing program is executed by the computation device 8. The image data 6 x is displayed on the monitor 7.

A sample having any of various dumbbell shapes defined in JIS can be used as the test sample S. Alternatively, a cut sample of an actual rubber product, an approximate model of a rubber product, or the like can be used. It is preferable to attach markers M to the surface of the test sample S. As the markers M, for example, markings in a color different from the color of the surrounding surface are used. A tensile strain generated in the test sample S can be easily determined by attaching the markers M at positions separated by a predetermined interval and by checking a separation distance between the markers M. In this embodiment, two test samples S are attached to the fixing frame 3, and the ozone resistances of the two test samples S are measured at the same time; however, there may be one test sample S or a plurality of test samples S. In a case where the ozone resistances of a plurality of test samples S are to be measured at the same time, the test samples S may have the same or different specifications.

The test tank 2 is a container, the inside of which can be sealed, and ozone Z is supplied from the ozone injector 4 such that the ozone concentration in the test tank 2 can be set to a desired concentration. For example, the ozone injector 4 is installed in a circulation path through which the ozone Z is supplied, and the circulation path is provided with an exhaust pipe or the like via an exhaust cleaning filter or a switching valve 4 a. Among wall surfaces of the test tank 2, a transparent resin or glass is used for a region facing the laser sensor 5 and the camera device 5 (the region required in order for the laser sensor 5 and the camera device 6 to detect and capture an image of the surface of the test sample S).

The fixing frame 3 enables placement of the test sample S under a preset placement condition. In this embodiment, both longitudinal end portions of the test sample S are clamped by gripping parts 3 a. For example, by attaching and fixing the test sample S to the fixing frame 3, the test sample S is maintained in a state in which a predetermined tensile strain is applied to the test sample S. Alternatively, a predetermined bending strain is applied to the test sample S to maintain the test sample S in a bent state. It is preferable to set the tensile strain applied to the test sample Sin accordance with the test method of JIS K 6259-1: 2015. The test sample S may also be placed in a state (form) that corresponds to the state in which a rubber product is actually used.

The laser sensor 5, with respect to the preset detection region of the surface of the test sample S placed in the test tank 2, detects, over time, the distance from the laser sensor 5 to the surface of the test sample S and acquires the detection data 5 x. As the laser sensor 5, a sensor that receives a laser beam, which has been emitted to the surface of the test sample S, and detects the distance to the surface is used. A movement mechanism is provided that moves the laser sensor 5 so as to cover the detection region.

The camera device 6 acquires the image data 6 x by capturing at a fixed point, over time, images of the surface of the test sample S that has been placed in the test tank 2. As the camera device 6, two types of a camera device, namely, a still image camera device and a video camera device, may both be used; however, either one of the two types may be used. The detection region covered by the laser sensor 5 and the image capture region covered by the camera device 6 are preferably the same region of the surface of the test sample S. For example, the region between the markers M is set to be the detection region and image capture region.

A predetermined detection data processing program is installed in the storage unit 9, and a database 10, in which the detection data 5 x is stored, is stored in the storage unit 9. An example of this detection data processing program is a program that identifies a detection position and size (distance) of the detection data 5 x, and calculates the disposition and size (length, volume, and area) of an ozone crack Cr (hereinafter referred to as “crack Cr”) on the surface of the test sample S.

The region in which a crack Cr occurs and the region in which a crack CR does not occur differ in terms of the size of the detection data 5 x. In other words, the separation distance between the surface of the test sample S and the laser sensor 5 before a crack Cr occurs is known. Then, when a crack Cr occurs, the laser beam emitted from the laser sensor 5 penetrates deep into the crack Cr and is reflected. Therefore, the detection data 5 x is larger in a region in which a crack Cr occurs than a region in which a crack Cr does not occur. Thus, by executing this detection data processing program by using the computation device 8, a region in which a crack Cr occurs and a region in which a crack Cr does not occur are distinguished from each other based on the magnitude of the detection data 5 x, and the disposition, volume, and area are identified and calculated.

In addition, a predetermined image data processing program is installed in the storage unit 9, and the database 10, in which the image data 6 x is stored, is stored in the storage unit 9. An example of the image data processing program is a program that identifies and calculates the disposition and area of each degree of shade (color) in the image data 6 x. A region in which an ozone crack Cr (hereinafter referred to as crack Cr) occurs and a region in which a crack Cr does not occur on the surface of the test sample S differ in terms of shade (color) in the image data 6 x. In general, a region in which a crack Cr occurs is darker than a region in which a crack Cr does not occur. Therefore, by executing this program by using the computation device 8, a region in which a crack Cr occurs and a region in which a crack Cr does not occur are distinguished from each other based on shade (color) in the image data 6 x, and the disposition and area thereof are identified and calculated.

In this embodiment, the image data processing program includes a sharpening program for the image data 6 x. This sharpening program performs processing such as increasing definition or refinement of the image data 6 and improving contrast so as to make it easy to see the image data 6 x that is difficult to see. As a result, it becomes easy to distinguish between a region in which a crack Cr occurs and a region in which a crack Cr does not occur based on shade (color) in the image data 6 x, which is advantageous for identifying and calculating the disposition and area of a crack Cr with high accuracy.

Next, an example of a procedure for evaluating ozone deterioration of a test sample S will be described.

As illustrated in FIGS. 1 to 3, test samples S are placed under a preset placement condition inside the test tank 2 having a predetermined ozone concentration. The inside of the test tank 2 is maintained at a predetermined ozone concentration. It is preferable to set the maintained ozone concentration to 500±50 ppb (50±5 pphm), 250±50 ppb (25±5 pphm), 1000±100 ppb (100±10 pphm), and 2000±200 ppb (200±20 pphm) in accordance with the test method of JIS K 6259-1: 2015. It is also possible to set the ozone concentration to one that approximates the conditions in which a rubber product is actually used.

The internal temperature and internal humidity of the test tank 2 are set to appropriate desired ranges. It is preferable that these conditions conform to the test method of JIS K 6259-1: 2015. Therefore, it is preferable that the internal temperature of the test tank 2 be set to 40±2° C. and the relative humidity at the internal temperature be 65% or less; however, it is also possible to set the internal temperature and the internal humidity to those that approximate the conditions in which a rubber product is actually used.

Then, with respect to the detection region of the surface of each of the test samples S placed in the test tank 2, a distance from the laser sensor 5 to the surface of the test sample S is detected, and the detection data 5 x is acquired. The detection data 5 x may be acquired 2, 4, 8, 24, 48, 72, and 96 hours after the start of testing in conformance with the test method of JIS K 6259-1: 2015; however, the time interval at which the detection data 5 x is acquired can be set as desired.

In this embodiment, images of the surface of the test sample S, which has been placed inside the test tank 2, are captured at a fixed point, over time, by at least one camera device 6, and the image data 6 x is acquired. The image data 6 x can be acquired 2, 4, 8, 24, 48, 72, and 96 hours after the start of testing in conformance with the test method of JIS K 6259-1: 2015; however, the time interval at which the image data 6 x is acquired can be arbitrarily set. In a case of a still image camera device, the acquisition of image data 6 x can be set to be performed at an interval of 10 minutes or at an interval of one hour, for example. In a case of a video camera device, the acquisition of the image data 6 x can be set to be performed successively, for example. Note that the detection data 5 x and the image data 6 x are preferably acquired at substantially the same timing in order to clarify the relationship therebetween.

The acquired detection data 5 x and the image data 6 x are successively input to the storage unit 9 and stored therein. The detection data 5 x and the image data 6 x that have been input to the computation device 8 are displayed on the monitor 7.

As a result of keeping the test sample S under a predetermined ozone concentration, the chemical bonds between the rubber molecules of the test sample S are broken. Consequently, as illustrated in FIG. 4, the surface state changes because cracks Cr occur on the surface of the test sample S. FIG. 4 illustrates image data 6 a, 6 b, 6 c, and 6 d acquired in the chronological order of (A), (B), (C), and (D), respectively.

Thus, based on the acquired detection data 5 x and the image data 6 x, the change in the surface state of the test sample S between the plurality of points in time is determined. For example, as the change in the surface state of the test sample S, at least one of the determination items among the total number of cracks Cr that have occurred per unit area, the total volume of cracks Cr that have occurred per unit area, and the total area of cracks Cr that have occurred per unit area can be calculated by the computation device 8 on the basis of the detection data 5 x.

In addition, as the change in the surface state of the test sample S, at least one of the determination items among the total number of cracks Cr that have occurred per unit area, the total area of cracks Cr that have occurred per unit area, the maximum length of cracks Cr that have occurred, the average length of cracks Cr that have occurred, the minimum length of cracks Cr that have occurred, and the length (or area) of a specific one or two cracks Cr can be calculated by the computation device 8 on the basis of the image data 6 x. In a case where the detection data 5 x and the image data 6 x are acquired, it is determined which data is preferentially used in order to calculate the above-described determination items.

FIG. 5 illustrates the change over time in the total volume of cracks Cr that have occurred per unit area of the test samples S (S1, S2, S3) having different rubber specifications. Since the depth of cracks Cr can also be detected by the laser sensor 5, the change in volume over time can be easily obtained by computation by the computation device 8.

FIG. 6 illustrates the change over time in the total area of the cracks Cr that have occurred per unit area of the test samples S (S1, S2, S3) having different rubber specifications. In this way, it is also possible to acquire a computation result by the computation device 8 for a desired determination item.

As described above, the detection data 5 x and the image data 6 x are acquired while the test sample S remains placed inside the test tank 2 having a predetermined ozone concentration. Then, since the change in the surface state of the test sample S between a plurality of points in time is determined on the basis of the acquired detection data 5 x and the image data 6 x, it is not necessary to remove the test sample S from and place the test sample S into the test tank 2 each time the surface state of the test sample S is to be checked. Observation of the surface of the test sample S with a microscope or the like is not required.

Moreover, according to the detection data 5 x, the depth and volume of the cracks Cr can also be determined. Therefore, according to the present invention, it is possible to accurately determine a change over time in the ozone deterioration of the vulcanized rubber material forming the test sample S while reducing the number of working man-hours.

Since the image data 6 x is digital data that is easy to analyze, a change over time in the surface state of the test sample S can be determined by analyzing the image data 6 x acquired at different points in time. Accordingly, as in this embodiment, by acquiring the detection data 5 x and the image data 6 x, it is possible to accurately determine a change over time in the surface state of the test sample S.

As illustrated in FIG. 7, each of the detection data 5 x and the image data 6 x is stored in the database 10 of the storage unit 9. The storage unit 9 stores indication data 11 x (11 a, 11 b, 11 c, . . . ), 12 x (12 a, 12 b, 12 c, . . . ) indicating the degree of progression of ozone deterioration. Then, it is also possible to automatically determine the degree of progression of ozone deterioration with respect to the surface state of the test sample S in each of the detection data 5 x on the basis of the indication data 11 x by comparing each of the detection data 5 x and the indication data 11 x by using the computation device 8. Similarly, it is possible to automatically determine the degree of progression of ozone deterioration with respect to the surface state of the test sample S in each of the image data 6 x on the basis of the indication data 11 x by comparing each of the image data 6 x and the indication data 11 x by using the computation device 8.

As the indication data 11 x, for example, data classified into a plurality of classifications in accordance with the size and depth of the volume of a crack Cr is used. For example, data classified as A classification, when the volume (depth) of a crack Cr is equal to or greater than a1 and less than a2, B classification, when the volume (depth) of a crack Cr is equal to or greater than a2 and less than a3, and C classification, when the volume (depth) of a crack Cr is equal to or greater than a3 and less than a4, and the like is stored as indication data 11 x in the storage unit 9. The computation device 8 selects the indication data 11 x that the detection data 5 x respectively matches. Accordingly, the surface state of the test sample S in the detection data 5 x is determined to be the degree of progression of ozone deterioration in which the selected indication data 11 x is classified.

As the indication data 12 x, for example, the indicator described in the method for evaluating cracks in an annex (standard) of JIS K 6259-1: 2015 is used. In other words, image data corresponding to the 15 classifications of A-1 to A-5, B-1 to B-5, and C-1 to C-5 described in this application is stored as the indication data 12 x in the storage unit 9. The computation device 8 selects the indication data 12 x having the highest degree of matching with each of the image data 6 x. Accordingly, the surface state of the test sample S in the image data 6 x is determined to be the degree of progression of ozone deterioration indicated by the indication data 12 x selected to have the highest similarity between images.

When two types of a camera device, namely, a video camera device and a still image camera device, are used as the camera device 6, it becomes easier to determine the state and degree of change in ozone deterioration in more detail. Similarly, in order to determine the state and degree of change in ozone deterioration in more detail, the degree of change in the surface state of the test sample S between a plurality of points in time is preferably determined using processed data obtained by performing sharpening processing on each of the image data 6 x.

In a case where a wall surface of the test tank 2 is interposed between the camera device 6 and the test sample S, noise may be included in the image data 6 x due to reflection of light from the wall surface and the like. Thus, as illustrated in FIG. 8, a through hole 2 a can be formed in the test tank 2, and an image capturing lens portion 6A of at least one camera device 6 can be inserted into the through hole 2 a from the outside to the inside of the test tank 2. A gap between an outer peripheral surface of the image capturing lens portion 6A and the through hole 2 a is sealed with a sealing material 2 b.

In this embodiment, the body of the camera device 6 is not disposed inside the test tank 2. This is advantageous in that sharper image data 6 x is acquired while preventing ingress of the ozone Z into the body of the camera device 6.

Each of the detection data 5 x and the image data 6 x can be successively input and stored in the storage unit 9 installed in a management office or the like away from the test tank 2, the laser sensor 5, and the camera device 6, via the Internet or the like. As a result, a change over time in the ozone deterioration of the surface of the test sample S (vulcanized rubber material) can be determined in the management office or the like.

REFERENCE SIGNS LIST

-   1 Evaluation system -   2 Test tank -   2 a Through hole -   2 b Sealing material -   3 Fixing frame -   3 a Gripping part -   4 Ozone injector -   4 a Switching valve -   5 Laser sensor -   5 x Detection data -   6 Camera device -   6A Image capturing lens portion -   6 x Image data -   7 Monitor -   8 Computation device -   9 Storage unit -   10 Database -   11 x, 12 x Indication data -   S Test sample -   M Marker -   Cr Crack -   Z Ozone 

1. A method, for evaluating ozone deterioration of a vulcanized rubber material, in which a test sample of a vulcanized rubber material is placed under a preset placement condition in a test tank having a predetermined ozone concentration and a change over time in a surface state of the test sample is determined, the method comprising: acquiring detection data by detecting, over time, with a laser sensor disposed facing a surface of the test sample that has been placed in the test tank, a distance from the laser sensor to the surface; and determining a change in the surface state of the test sample between a plurality of points in time, based on the detection data.
 2. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 1, wherein, as the change in the surface state of the test sample, at least one determination item among a total number of ozone cracks that have occurred per unit area, a total volume of ozone cracks that have occurred per unit area, and a total area of ozone cracks that have occurred per unit area is determined.
 3. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 1, further comprising: storing each of the detection data in a database of a storage unit; and automatically determining, by comparing indication data indicating a degree of progression of ozone deterioration stored in the storage unit and each of the detection data by using a computation device, the degree of progression of ozone deterioration with respect to the surface state of the test sample in each of the detection data, based on the indication data.
 4. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 1, further comprising: acquiring image data, which is digital data, by capturing at a fixed point, over time, images of the surface of the test sample with at least one camera device, the change in the surface state of the test sample between the plurality of points in time being determined based on the image data.
 5. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 4, wherein the change in the surface state of the test sample between the plurality of points in time is determined using processed data obtained by performing sharpening processing on each of the image data.
 6. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 4, further comprising: storing each of the image data in a database of a storage unit; and automatically determining, by comparing indication data indicating a degree of progression of ozone deterioration stored in the storage unit and each of the image data by using a computation device, the degree of progression of ozone deterioration with respect to the surface state of the test sample in each of the image data, based on the indication data.
 7. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 4, wherein, as the change in the surface state of the test sample, at least one determination item among a total number of ozone cracks that have occurred per unit area, a total area of ozone cracks that have occurred per unit area, a maximum length of ozone cracks that have occurred, an average length of ozone cracks that have occurred, a minimum length of ozone cracks that have occurred, and a length or area of a specific ozone crack that has occurred is determined.
 8. The method for evaluating ozone deterioration of a vulcanized rubber material according to claim 4, wherein a through hole is formed in the test tank, and an image capturing lens portion of at least one of the camera devices is inserted into the through hole from outside to inside the test tank, a gap between an outer circumferential surface of the image capturing lens portion and the through hole is sealed, and the image data is acquired.
 9. A system, for evaluating ozone deterioration of a vulcanized rubber material, in which a test tank is maintained at a predetermined ozone concentration and a fixing frame enables placement of a test sample of a vulcanized rubber material under a preset placement condition in the test tank, the system comprising: a laser sensor disposed facing a surface of the test sample that has been placed in the test tank; a storage unit into which detection data of a distance from the laser sensor to the surface, which is detected over time by the laser sensor, is input; and a computation device configured to execute a predetermined detection data processing program, a degree of change in a surface state of the test sample between a plurality of points in time being calculated by the computation device, based on the detection data. 